In the photocopying field, it is common to project an image of an original object onto a moving light-sensitive medium by means of moving optical devices in such a manner that no relative movement takes place between the reproduced image and the moving medium. Such a device is described in German Offenlegunsschrift No. 1,497,089, for example. In this device, the object is scanned by means of an oscillating pivotable mirror and reproduced on a synchronously moving light-sensitive medium. Another known system uses a planar support plate for the object and an arrangement of two groups of mirrors which scan the object while maintaining a constant optical path and also project an image of the object on a light-sensitive medium moving in synchronism thereto. The two mirror groups are moved at different speeds. Such a device is described in German Patent Specification No. 1,215,503. Finally, it is possible to move the object itself in synchronism with the light-sensitive medium and to reproduce the image of the object on the medium.
In electrophotographic apparatus using such a strip-wise scanning of the object, accurate exposure of the scanned strip portion is normally quite critical. The gap width, the speed of travel of the light-sensitive medium, and the medium sensitivity determine the radiation intensity for the object. Various devices have been developed to increase the light yield in arrangements of the above kind. The aim of such measures always has been to achieve higher numbers of copies per minute with light sources of economically reasonable power requirements. For this purpose, spaced parallel fluorescent tubes are moved in synchronism with scanning along the object, which tubes illuminate the gap to be scanned between themselves. Curved mirrors have also been used in connection with such fluorescent tubes to further increase the radiation intensity. Finally, it has also been disclosed for scanning with a pivotable mirror to arrange a greater number of fluorescent tubes on both sides of the total zone scanned by the scanning beams in order to achieve a uniform and intense illumination of the original.
All those devices, however, have not been completely satisfactory since the light sources lead to locally different intensities of illumination and allow an increase of the copying speed only in connection with a technically and economically unreasonable increase of the lamp output.
A further disadvantage of known exposure arrangements resides in heat development. An increase of the lamp output results in a considerable and troublesome heating of the support plate for the object and of the structural elements in the vicinity thereof.
The present invention was developed to provide an exposure arrangement which is characterized by great simplicity and safety in operation, which overcomes the disadvantages of the known devices and which simultaneously can operate by means of commerical point light sources of highest performance.